A disc drive includes a plurality of stacked discs which are rotationally supported relative to a disc spindle and an actuator assembly movably supporting a plurality of head gimbal assemblies for reading and writing data to the discs. The actuator assembly includes an actuator drive typically a voice coil motor for actuating the head gimbal assemblies relative to selected data tracks of the discs.
The voice coil motor includes a magnet assembly defining a permanent magnetic field and a energizable coil coupled to an actuator block supporting the head gimbal assemblies. Current is supplied through the coil to selectively operate and move the actuator block to align the head gimbal assemblies relative to predetermined data tracks of the discs. A typical magnet assembly includes upper and lower pole plates or backirons which are supported relative to the disc drive assembly in a spaced relation and include a magnet coupled thereto to define a flux gap therebetween. An energized coil moves in the flux gap between the upper and lower pole plates.
For proper operation of the voice coil motor, the magnets must be accurately aligned and assembled to upper and lower pole plates. Alignment of magnets on the pole plates may be measured for quality control. Measurement instruments may be used to measure alignment of magnets by measuring the distance between the transition zone of a magnet bonded to a pole plate and a reference point. However, in order to rely on such measurements for quality control, the measurement instrument must provide a relatively accurate dimension measurement. If the measured dimension is different from the actual dimension, then quality control is compromised. The present invention addresses these and other problems, and offers advantages over the prior art.